Conan joked on his show about Justin disrespecting a picture of Bill Clinton, saying, “Justin Bieber apologized to President Clinton for what he did to his photo. In return, Clinton apologized for what he did to a photo of Selena Gomez.”

A source close to Justin told HollywoodLife.com EXCLUSIVELY that Justin heard about Conan’s joke and fired back with his own diss, saying, “What is a Conan?”

“Justin doesn’t care because he thinks nobody watches or cares about Conan O’Brien,” our source reveals. “He isn’t going to give him the time of day to make his comments mean anything. People make fun of Justin all the time. He isn’t taking it to heart.”

Justin Bieber Is Angry About Conan O’Brien’s Diss

Despite what our source tells us, Justin must have been at least a little bothered by Conan’s diss because he chose to reply to it. Maybe because Conan insulted not only Justin, but the Biebs’ girlfriend, Selena,by making a seriously gross joke about Sels, 20, and Bill, 66. We think it’s sweet that Justin came to Selena’s defense.

HollywoodLifers, who do YOU think had the last laugh, Justin or Conan?